Organisers

• Riccardo Rurali (Universitat Autònoma de Barcelona)
• Mads Brandbyge (Denmark Technical University)
• Xavier Blase (Université Claude Bernard-Lyon 1 and CNRS)

Supports

 CECAM

 Psi-k

 COST - MolSimu

Description

The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology. Like carbon nanotubes, nanowires represent an excellent test-bed of how the quantum effects determine their geometric and electronic structure and, especially, their electron transport properties.
With the continuous miniaturization of electronic devices the search for building blocks of future molecular electronics application have attracted a great interest and nanowires seem to be one of the most promising alternative. The great advantage that they present over carbon nanotubes is that they are invariantly semiconducting, while, as it is well known, carbon nanotubes are metallic or semiconducting depending on their chirality that, to date, cannot be controlled at growth time. This is an essential feature for the design and realization of nanoelectronics applications, which require basic components that are semiconductors. Hence, not only nanowires can be used as interconnections between different components, but they can also directly operate as the active region of the device and several examples of (nano)transistors have been demonstrated.
However, an exhaustive physical understanding of many fundamental issues, such as the influence of the structure on the conducting properties, the role of surface conduction or defect scattering, is still lacking. A crucial mechanism like the contribution of extrinsic carriers (those provided by dopants) to the conduction, for instance, is far to be fully understood in systems of low dimensionality and nanoscopic sizes like nanowires and basic questions such as the radial localization of impurities, their ionization energy in the confined nanowire geometry, and their ability to trap states, are still largely unanswered. The difficulties inherent to the density functional theory to calculate excitation energies are a serious difficulty to address part of these questions.
The role of theoretical modeling and simulation is extraordinarily important, since many of the properties of nanowires only difficultly can be accessed experimentally. As a matter of fact, although the structure of the most common nanowires is reasonably well-know, thanks to several theoretical studies and experimental works, relatively little is known about the structure and the electronic properties in less conventional, but equally interesting situations, such as (i) heterostructures, lattice mismatch, strained structures, (ii) growth / deposition on surfaces (iii) stability, diffusion and electronic properties of defects and (iv) spin-transport in presence of magnetic impurities/leads. All these situations have the highest interest, and they are far to be satisfactorily understood.
Concerning silicon nanowires in particular, it must be underlined that wires grown along most of the crystallographic orientations exhibit a direct band-gap, while it is well-know that in bulk silicon is indirect. This circumstance opens a brand new research line which, obviously, has already attracted the interests of a large part of the nanoelectronics community: the realization of silicon-based optics and optoelectronics applications.

Scientific Objectives

Despite the great importance of this research field, both from the fundamental physics and the nanoelectronics viewpoints, we have detected a lack in the international conference and workshop scenario of a meeting devoted to it. We have decided to bring together the leading theoreticians working on nanowires, covering all the main aspects related with them, including the study of the structural, electronic and transport properties.
The topic of the workshop that we propose is slightly wider and refers to "quantum wires". The idea is to open the meeting to a larger class of system, though obviously intimately related, including one-dimensional electron systems (1DEG) at surfaces and mono-atomic metallic chains.
We expect the workshop to be extremely useful to clarify the state-of-the-art of several crucial problems that might prevent the advance of this research field, such as the role of doping and its activation, the scattering by impurity, the electron-phonon coupling, the performances of nanowires-based transistors and the use of nanowires for different sensor applications.
The community involved ranges from solid-state physicists and quantum chemists working on the atomistic modeling of nanowires at the first-principles level, to electrical engineers developing compact models of nanowires-based devices. Although the focus of the meeting will be on the theoretical modeling of such systems, we are convinced about the need to enlarge the audience to experimentalists who will share their experience and rationalize their need in further theoretical developments.

References

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[3] Cui, Yi and Lieber, Charles M. Functional Nanoscale Electronic Devices AssembledUsing Silicon Nanowire Building Blocks, Science 291 851--853 (2001)

[4] Fernando Patolsky and Charles M. Lieber Nanowire nanosensors, Materials Today 8 20--28 (2005)

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[7] Mads Brandbyge and Jose-Luis Mozos andPablo Ordejon and Jeremy Taylor and Kurt Stokbro Density-functional method for nonequilibriumelectron transport, Phys. Rev. B 65 165401 (2002)

[8] Thomas Frederiksen and Mads Brandbyge andNicolas Lorente and Antti-Pekka Jauho Inelastic Scattering and Local Heating in AtomicGold Wires, Phys. Rev. Lett. 93 256601 (2004)

[9] Rurali, R. and Lorente, N. Metallic and Semimetallic Silicon $langle 100rangle$ Nanowires, Phys. Rev. Lett. 94 026805 (2005)

[10] Singh, A.K. and Kumar, V. and Note, R. andKawazoe, Y. Effects of Morphology and Doping on the Electronicand Structural Properties of HydrogenatedSilicon Nanowires, Nano Lett. 6 920--925 (2006)

[11] Fernandez-Serra, M.-V. and Adessi, Ch.and Blase, X. Conductance, Surface Traps, and Passivation inDoped Silicon Nanowires, Nano Lett. 6 2674--2678 (2006)

[12] T. Vo and A. J. Williamson and G. Galli First principles simulations of the structuraland electronic properties of silicon nanowires, Phys. Rev. B 74 045116 (2006)

[13] Stern, Eric and Klemic, James F. and Routenberg,David A. and Wyrembak, Pauline N. andTurner-Evans, Daniel B. and Hamilton, Andrew D.and LaVan, David A. and Fahmy, Tarek M. andReed, Mark A. Label-free immunodetection with CMOS-compatiblesemiconducting nanowires, Nature 445 519--522 (2007)

[14] R. He and P. Yang Giant piezoresistance effect in siliconnanowires, Nat. Nanotechnol. 1 42--46 (2006)

[15] Troels Markussen and Riccardo Rurali andAntti-Pekka Jauho and Mads Brandbyge Scaling Theory Put into Practice: First-PrinciplesModeling of Transport in Doped Silicon Nanowires, Phys. Rev. Lett. 99 076803 (2007)